Web guide



April 30, 1963 D. N. STREETER 3,087,664

WEB GUIDE 7 Filed Oct; 17, 1960 2 Sheets-Sheet 1 FIG.2

INVENTOR DONALD N. ST-REETER V ahn-moi.

AGENT- April 1963 D. N. E aTREETER 3,087, 6 64- WEB GUIDE Filed Oct. 17, 1960 2 Sheets-Sheet 2 A g W FIG.4

United States Patent Oflice 3,087,664 Patented Apr. 30, 1963 3,087,664 WEB GUIDE Donald N. Streeter, Wayland, Mass, assignor to International Business Machines Corporation, New York, N.Y., a corporation of New York Filed Oct. 17, 1960,, Ser. No, 62,960 2 Claims. (Cl. 226-97) This invention relates to a means for guiding webs and more particularly to a means for guiding webs without frictionally contacting the webs.

The transporting of webs at very high speeds, especially thin and fragile webs such as magnetic tapes, has posed problems due to the friction between the apparatus transporting the webs and the delicate surface and sides of the webs. Part of this problem has been overcome in the art by using air-lubricated web transporting devices, that is, devices wherein. air under pressure is exhausted through the surface of the device causing the web to float above the surfiace on a cushion of These air-lubricated web transporting devices solve the problem of friction between the surface of the web andthe, surfiace f fl fi dfl but do not solve the. problem of guiding the web without frictional contact with the sides of the, web. Sometimes flanges are placed on the edge of these air-lubricated web transporting devices to guide the movement of the web by mechanical engagement of the sides of the web with the flanges of the device; Such mechanical engagement causes wear on the sides of the web due to friction.

Still other air-lubricated web transporting devices in the art solve the problem of guiding the web without frictional contact between the sides of the web and the device by directing the air being exhausted from the surface of the device so as to form a V-shaped trough of The Web rests in the center of the 'V-shaped trough and air is exhausted in substantially equal quantities about the two sides of the web. When the web moves laterally to one side of the center of the V-shaped trough, the air rushing up this side of the V-slraped trough impinges on the surface of the web causing it to rise up from the surface of the device. Tensile stress in the web limits the raising motion of the web and causes it to return to the center of the V-shaped trough of air.

Forming the V-shaped trough of air requires intricate air directing mechanisms including orifices cut at angular relationships to each other in the surface of the airlubricated web transporting device. Also, a nonuniform tension is produced across the web to whatever degree the tape conforms to the V-shaped trough. This nonuniform tension is known to create excessive wear upon magnetic reading and writing heads and upon the web itself.

The present invention is an improved air-lubricated web transporting device. The principle of operation is founded upon the discovery that the web can be laterally guided by two distinctly diiierent types of forces exerted on the surface of the Web. The first type of force, viscous shear, is caused by the flow of air parallel to the surface of the web and is somewhat like the force developed on the surface of wood by rubbing sandpaper over it. The second type of force is due to pressure and acts normal to the surface of the web. The present invention discloses a means for harnessing these two forces so that the web is guided and supported without frictional contact with any 2 part of the device. The device is a simple, but unobvious, combination of parts which cooper-ate with the web to variably impede the flow of air about the web so that a net force due to viscous shear caused by the flow of air tends to recenter the web, and at the same time, the parts co.- operate to build up pressure in the proper location so that a net force due to pressure also tends to recenter the web. Lateral recentering of the web is accomplished by the means shown in the present invention without the requirement of additional tensile stresses being developed in the web due to the recentering forces. Additionally, the web need not be of a laterally flexible material or a tor-sionally flexible material since the recentering force due to viscous shear is capable of operating on a flat web.

Accordingly it is an object of this invention to provide a device simple in construction for guiding webs without frictional contact.

Another object of this invention is to provide a device for guiding and recentering webs without requiring additional tensile stresses to be developed in the web.

A further object of the invention is to provide a device for guiding webs composed of material which is not laterally flexible, or torsionally flexible.

Still another object of the invention is to provide a device for guiding webs with a high degree of accuracy,

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a front view of a magnetic tape transporting system.

FIG. 2 is a perspective view of a section of a structure. embodying the invention.

FIGS. 3 through 7 are sectional views of the structure shown in FIG. 2 with the clearance dimensions between the tape 1 and structure 5 greatly exaggerated.

The present invention can be used in any web transporting system. The system shown in FIG. 1 illustrates the manner in which the invention may be employed to guide a web. The web in this illustration is a magnetic tape I wound on reels 2 and 3 and driven by capstans 20 and 21 and pressure rollers 22 and 23. The object of the system is to transport the tape 1 past the transducer head 4. During the travel of tape 1 from reel 2 to reel 3, it is guided by the two identical structures 5 and 6 which embody the present invention. The structures 5 and 6 are supplied with compressed air from compressor 9 through conduits 7 and 8. The compressed air is exhausted through the structures 5 and 6 in a manner to be described in detail so that the tape is guided without frictional contact with the structures 5 and 6.

In FIG. 2, the details of the structure 5 are shown. The advantageous parts of the structure 5 are the flanges 10 and 11, which cooperate with the tape .1 to impede the flow of air. The manner in which these parts co operate with the tape 1 will be described below. Compressed air from conduit 7 in FIG. 1 is delivered to the port 14 in FIG. 2. Pressure is developed in the chamber between plates 15 and =16 (cut away portion of plates 15 and 16 shown in FIG. 2.).

FIG. 3 is a cross sectional vieW of the structure shown in FIG. 2 taken along the center line of the slot 13. The

distances between the tape and structure are greatly exaggerated to aid in the explanation to follow. The tape 1 is shown floating above the surface 12. The tape is supported in this position by the air exhausted from the slot 13, the solid arrows indicating the direction of flow of air. The air impinging on the bottom of the tape 1 cfeates the supporting pressure. The length of the slot 13 may be varied depending on the degree to which the tape 1 is required to bend around the structure 5.

FIG. 4 is a cross sectional View of the structure in FIG. 2 taken perpendicular to the slot 13. The tape 1 is shown in the equilibrium position centered about the slot 13. The air flows in substantially equal quantities about both sides of the tape because the impedance to the flow of air is equal.

In FIG. 5 the tape 1 is shown laterally displaced to the left of the equilibrium position. The impedance to the flow of air with the tape 1 in this position is unbalanced. This unbalanced impedance is due to the close proximity of the tape 1 to the flange and the large opening between the tape 1 and the flange 11. The unbalanced impedance causes a major portion of the air to flow through the opening between the tape 1 and the flange 11. Therefore, the velocity of the air moving to the right is higher than the velocity of the air moving to the left of slot 13. The farther the tape 1 moves away from the equilibrium position the more unequal the flow of air becomes about the tape. The movement of air along the bottom surface of the tape causes a force to be exerted on the tape in the direction of motion of the air. This force is the result of a phenomenon known as viscous shear between the tape and the moving air. As the velocity of the air becomes greater, the force due to viscous shear becomes greater. Therefore the net force on the tape in FIG. 5 due to the flow of air is toward the right, tending to recenter the tape over the slot 13. If the tape should overshoot the slot 13 and move toward the right of the equilibrium position, a major portion of the air flows to the left of the slot resulting in a net force to the left due to viscous shear.

The tape in FIG. 6 is shown to the left of the equilibrium position. In this figure the recentering force due to pressure alone is illustrated. The force due to pressure is indicated by the dotted arrows and acts normal to the bottom surface of tape 1 as shown. The length of the dotted arrows indicates approximately the relative magnitude of the pressure. The force due to pressure exerted on the tape 1 in FIG. 6 is caused by the pres sure differential between the atmospheric pressure above the tape 1 and the compressed air pressure below the tape 1. Due to the close proximity of the tape 1 to the flange 10 a large pressure differential is maintained on this edge of the tape 1. The open space between the tape 1 and flange 11 allows the pressure on this edge of the tape 1 to drop toward atmospheric pressure. The loss in pressure differential decreases the support beneath the tape 1 on this side. When the tape 1 is made of a latterally flexible material, it bends downward as shown in FIG. 6. Since the force due to pressure acts normal to the surface of the tape, there is a lateral component of force tending to recenter the tape 1.

In FIG. 7 a tape 1 made of torsionally flexible material, that is a tape capable of twisting along its longitudinal axis but not capable of bending across its width, is shown to the left of the equilibrium position. Due to the build up of static pressure under the left side of the tape 1 as described in connection with FIG. 6, the tape assumes a twisted position as shown in FIG. 7. A lateral component of force due to pressure tends to recenter the tape 1.

The specific embodiment of the invention shown in FIGS. 2-7 is capable of guiding a laterally nonflexible and a torsionally nonflexible tape since the force due to viscous shear as illustrated in FIG. 5 is capable of recen- 4 tering the tape 1 even though it is flat and parallel to the surface 12. Since, as illustrated in FIGS. 4-7, the tape 1 does not raise up from the surface 12 during its excursions from the equilibrium position, recentering is accomplished without additional longitudinal tensile stress in the tape 1.

The dimensions of the structure 5 are important since there must be a proper balance of impedance to the flow of air about edges of the tape 1. It has been discovered that for most effective operation of the invention the clearance between the tape 1 and flanges 10 and 11 should be of the order of magnitude of the clearance between the surface 12 and the tape 1 in its equilibrium position. It is also apparent that the height of the flanges 10 and 11 should be sufficient to extend above the tape 1 when the tape is in the supported position above the surface 12 so that the proper cooperation between the tape 1 and flanges 10 and 11 is achieved.

The following table shows, by way of example, particular dimensions of the structure 5 shown in FIGS. 2-7 found to be suitable for guiding a tape whose width is 1.000 inch and thickness is 0.002 inch. These values are set forth by way of example only and the invention is not limited to them nor any of them.

Table Distance between flanges 10 and 11 inches 1.005 Width slot 13 located midway between flanges 10 and 11 inch 0.015 Height of flanges '10 and 11 above surface 12 Radius of curvature of surface 12 ..-do 1.250

The opening in the surface 12 is not limited to the shape of a slot, but may be any one or more orifices between the flanges 10 and 11 through which air is exhausted in substantially equal quantities about the edge of the tape 1 when in the equilibrium position.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the in vention.

I claim:

1. Apparatus for guiding and supporting a web without mechanical contact between said web and said apparatus comprising; a surface having one or more air orifices cut therein, means for exhausting air under pressure through said orifices against the lower side of said web, two substantially parallel flanges mounted upon said surface normal thereto one on either side of said orifices so that said one or more orifices are centrally located, said flanges being of sufficient height to extend above said web when said web is located between said flanges in a position supported above said surface by said air exhausting from said orifices, the distance between said flanges being slightly greater than the width of said web forming a clearance between the edges of said web and said flanges in the order of magnitude of the clearance between the web and said surface when said web is in said supported position, the amount of said clearance being selected so that lateral movement of said web toward one of said flanges creates an unbalanced impedance to the flow of said air about the edges of said web resulting in a net flow of said air toward the other of said flanges returning said tape to a center position between the flanges.

2. Apparatus for guiding and supporting a torsionally nonflexible and laterally nonflexible web without mechanical contact between said web and said apparatus comprising; a surface having a slot cut therein, means for exhausting air under pressure through said slot, against the lower side of said web, two substantially parallel flanges mounted upon said surface normal thereto each being an equal distance from said slot and parallel to said slot, said flanges being of suflicient height to extend above said web when said web is located between said flanges in a position supported above said surface by said air exhausting from said slot, the distance between said flanges being slightly greater than the width of said web resulting in a clearance between the edges of said web and said flanges in the order of magnitude of the clearance between the web and said surface when said web is in said supported position, the amount of said clearance being selected so that lateral movement of 5 position between said flanges.

References Cited in the file of this patent UNITED STATES PATENTS 1,629,154 DeYbarrondo May 17, 1927 2,848,820 Wallin et a1. Aug. 26, 1958 2,908,495 Andrews et a1 Oct. 13, 1959 2,954,911 Baurneister et a1. Oct. 4, 1960 2,967,674 Lawrance et a1. Jan. 10, 1961 2,032,246 Fritze May 1, 1962 

1. APPARATUS FOR GUIDING AND SUPPORTING A WEB WITHOUT MECHANICAL CONTACT BETWEEN SAID WEB AND SAID APPARATUS COMPRISING; A SURFACE HAVING ONE OR MORE AIR ORIFICES CUT THEREIN, MEANS FOR EXHAUSTING AIR UNDER PRESSURE THROUGH SAID ORIFICES AGAINST THE LOWER SIDE OF SAID WEB, TWO SUBSTANTIALLY PARALLEL FLANGES MOUNTED UPON SAID SURFACE NORMAL THERETO ONE ON EITHER SIDE OF SAID ORIFICES SO THAT SAID ONE OR MORE ORIFICES ARE CENTRALLY LOCATED, SAID FLANGES BEING OF SUFFICIENT HEIGHT TO EXTEND ABOVE SAID WEB WHEN SAID WEB IS LOCATED BETWEEN SAID FLANGES IN A POSITION SUPPORTED ABOVE SAID SURFACE BY SAID AIR EXHAUSTING FROM SAID ORIFICES, THE DISTANCE BETWEEN SAID FLANGES BEING SLIGHTLY GREATER THAN THE WIDTH OF SAID WEB FORMING A CLEARANCE BETWEEN THE EDGES OF SAID WEB AND SAID FLANGES IN THE ORDER OF MAGNITUDE OF THE CLEARANCE BETWEEN THE WEB AND SAID SURFACE WHEN SAID WEB IS IN SAID SUPPORTED POSITION, THE AMOUNT OF SAID CLEARANCE BEING SELECTED SO THAT LATERAL MOVEMENT OF SAID WEB TOWARD ONE OF SAID FLANGES CREATES AN UNBALANCED IMPEDANCE TO THE FLOW OF SAID AIR ABOUT THE EDGES OF SAID WEB RESULTING IN A NET FLOW OF SAID AIR TOWARD THE OTHER OF SAID FLANGES RETURNING SAID TAPE TO A CENTER POSITION BETWEEN THE FLANGES. 